Q: We're seeing the appearance of small cracks in our suction liner and impeller. The wear is unusual and seems premature. What's going on?
A: During pump operation, the bearing housing is exposed to extremely high thrust loads that apply force forward. If the bearing assembly hold-down bolts are not tight, the bearing housing will move forward, causing the impeller to rub against the suction liner.
- Rubbing causes heat.
- Heat causes cracks.
- Cracks lead to catastrophic failures of the impeller and the suction liner.
- Catastrophic failure causes unscheduled downtime — and drives costs up!
You can prevent this problem with one simple action: Use the recommended amount of torque when tightening the bearing assembly hold-down bolts.
To ensure that the bearing assembly doesn't move, take these steps:
- Clean the threads on the bolts and nuts. Make sure pedestal saddles are clean and free from any wax or lubricants.
- Replace any fasteners that show signs of damage, wear, or galling.
- Coat the threads with either copper- or nickel-based anti-seize. If an alternative lubricant is used, torque values must be adjusted accordingly.
- Use a heavy-duty industrial torque wrench to tighten the bolts. Standard air wrenches provide only about half the torque required.
How do you know how much torque you need? It's easy: Each GIW pump has a plate on the side that tells you how much torque is needed to keep the bearing assembly in place. This information can also be found in the GIW maintenance manual.
Correct bearing assembly hold-down bolt torque will keep the bearing housing from moving forward under normal operation and will eliminate the chance of rubbing and premature impeller and suction liner failures.